Studies on sensory and motor mechanisms in mammalian and reptilian muscle spindles are proposed. The role of mechanical factors and possible conductance changes in the production of the receptor potential will be studied in isolated muscle spindles. The characteristics of the impulse initiating site will be studied by applied current of varied slope. Motor responses will be studied by recording muscle contraction following motor nerve stimulation using high speed photography and differential interference optics as well as microelectrode recording. Studies on Golgi tendon organs are also proposed.